This invention relates to a grate assembly for a boiler of the type known as a shell boiler, herein referred to as the type described, and comprising a tubular shell with its axis arranged horizontally with one or more furnace tubes extending inwardly from the front end of the shell with each furnace tube being mounted at its rear end in an opening in the front wall of a combustion chamber. The invention also relates to a boiler of the type described including a grate assembly.